True Believers: folks with a capital-V Vision, who oversimplify issues in trying to argue for what they "know".

Me: with age and, alas, bitter experience I'm Dr. Disclaimer, Nuance Man, Mr. Footnote, the Quibbler, Sir Counterexample. I have to hold myself back in discussions to avoid raising obnoxious "on the other hand" objections. Often I fail.

TrueNames: a seminal sf short novel by VernorVinge. Sometimes it comes to mind when I'm in the company of zealots. Near the beginning of the story one of my favorite characters — the "Slimey Limey" — describes a clever hack he's done. Another character suggests a flaw through which the Limey's secret identity might be uncovered. My hero explains why that won't work:

The Limey made a faffling gesture. "It's actually a wee bit more complicated. Face it, chums, none of you has ever come close to sightin' me, an' you know more than any Mafia."

That was true. They all spent a good deal of their time in this plane trying to determine the others' True Names. It was not an empty game, for the knowledge of another's True Name effectively made him your slave — as Mr. Slippery had already discovered in an unpleasantly firsthand way. So the warlocks constantly probed one another, devised immense programs to sieve government personnel records for the idiosyncracies that they detected in each other. At first glance, the Limey should have been one of the easiest to discover: he had plenty of mannerisms. His Brit accent was dated and broke down every so often into North American. Of all the warlocks, he was the only one neither handsome nor grotesque. His face was, in fact, so ordinary and real that Mr. Slippery had suspected that it might be his true appearance and had spent several months devising a scheme that searched U.S. and common Europe photo files for just that appearance. It had been for nothing, and they had all eventually reached the conclusion that the Limey must be doubly or triply deceptive.

I can identify with the Slimey Limey. He's not a cardboard virtual-reality caricature. He has flaws, subtleties, twists. He's adaptable, agile, a survivor. His personal goals are modest. And in connection with him, Vinge uses delightfully oblique words like "faffling". The Limey is "... a wee bit more complicated." Who could resist?